1. Field of the Invention
The present invention relates to an apparatus for the continuous real time analysis of particulate matter in gases and, more particularly, for the quantitative determination of particulates in an exhaust gas from a diesel engine.
2. Description of Related Art
The analysis of particulates in gases has usually required the collection of the particulates in a filter and a subsequent weighing of the particulates by a precise weight balance. For example, in an appointed volume of a high temperature exhaust gas discharged from a diesel engine, the exhaust gases have been introduced into a gas passageway to collect particulates by means of a collecting filter positioned in the gas passageway. The filter is then weighed with a precision balance and, knowing the previous weight of the filter without the particulate material, a determination can be made of the quantity of particulates that exist in the predetermined volume of the exhaust gas. This provides a quantitative analysis on the basis of a difference between the filter weight before collection of the particulates and the filter weight after collecting the particulates.
However, problems have occurred in these procedures, since water s frequently a by-product in the combustion gas of the diesel engine, and as water can be absorbed on the filter to provide an error in measurement. That is, the weight of the water will be mistaken for particulate material. A solution to this problem has been to soak the filter at constant temperature and humidity for several hours prior to use so that the weight of the filter and the water both before and after collecting the particulates will be the same. Additional problems, however, exist in that a volatile HC component known as sof (soluble organic fraction), soluble in the usual organic solvents, C components called dry soot, sulfate, and the like, are frequently contained in the particulates and the sof components must be extracted with organic solvents, while the sulfate particulates must be extracted with distilled water or by an eluting solution for use in an ion chromatography. As can be readily determined, it takes a long time period to complete such a measurement and to resolve the problems. This also requires a fairly high skill level in the work staff with potentials for errors so that individual operators can provide different analytical results.
In addition, the filter in which the particulates have been collected must be removed from the gas passageway. Thus, a disadvantage occurs in that a continuous measurement, or a real time measurement, cannot be effectively obtained. Thus, the ability to measure the different particulates that would occur under different load levels on the engine becomes difficult to measure.
Attempts have been made to provide particulate mass monitors for detecting the change of mass when the particulates are collected on the filter, such as a change of the residence frequency of a pipe and the like. Additionally, a Hertridge-type smoke meter, in which light is incident upon the particulates to measure a transmittance of the light, has also been developed as an alternative method of continuously measuring the particulates in diesel engine combustion gases.
Problems still remain, however, in such methods, such as the sof components cannot be measured distinctly from the dry soot, and these alternative methods are insufficient to the more commonly used method of collecting by means of a filter and weighing the filter on a weight balance. Accordingly, the prior art is still seeking to improve the methods and systems for measuring particulates in a gas combustion source.